1. Field of the Invention
The present invention relates to a mobile handset and, in particular, to a dual mobile handset supporting Code Division Multiple Access (CDMA) and Global System for Mobile communication (GSM) and a call processing method for the dual mode mobile handset.
2. Description of the Related Art
The mobile communication systems are generally classified into two categories, i.e. an asynchronous GSM system, which is primarily used in Europe, and a synchronous CDMA system, which is primarily used in North America. The CDMA system is characterized in that a transmitter and a receiver are synchronized using a Global Positioning System (GPS).
The GSM system uses a combination of Frequency Division Multiple Access (FDMA) and Time Division Multiple Access as a multiple access method. GSM is the most popular standard for mobile communication in the world such that developments of GSM services are profitable.
CDMA system is a representative synchronous mobile communication system and uses a spread spectrum technology. The spread spectrum is advantageous in terms of increasing frequency reuse. Since CDMA cells use the same frequency band, soft handover is possible between the cells in addition to high frequency reuse efficiency. Also, CDMA uses code channels, which increases security and privacy protection.
The two communication standards use different frequency bands with different specifications such that a CDMA mobile handset and a GSM mobile handset are not compatible. That is, a CDMA mobile handset is useless in a GSM service area, and a GSM mobile handset cannot be used in a CDMA area.
Accordingly, when a person travels from a CDMA service area to a GSM service area and vice versa, the person must change his or her mobile handset or carry two types of mobile handsets.
In order to solve this problem, dual mode mobile handsets have been developed. Such conventional dual mode mobile handsets must be booted in one of the GSM and CDMA modes. However, in regions such as China and Brazil where both the CDMA and GSM networks are mingled, the conventional dual mode mobile handset is used as a single mode mobile handset only for the communication system selected by the user. That is, the conventional dual mode mobile handset cannot receive CDMA and GSM services at the same time.